Properties of thyrotrophin receptors in human thyroid membranes.

The influence of pH, salts, temperature and time of incubation on the binding of [125I]thyrotrophin to its human thyroid receptor was studied. Optimal binding was achieved at pH 7.0--7.6. Pre-incubation of membrane receptors at pH 6.0 resulted in a 60% loss of binding. There was dynamic equilibrium, as demonstrated by kinetic experiments. Scatchard analysis yielded non-linear plots with apparent affinity constants of 1.9 x 10(9) M-1 and 3.7 x 10(7) M-1. The concentration of [125I]thyrotrophin used in the experiments (1.2--2.2 pM) approximated normal human serum thyrotrophin concentration.